On Wed, Nov 10, 2010 at 12:47 AM, Shaping <[email protected]> wrote:
> I tried the first two yellow blocks in this article
>
> http://www.bluishcoder.co.nz/2007/11/embedded-grammars-in-factor.html
The syntax has changed quite a bit since that post. The example would
now be something like:
EBNF: expr
digit = '1' | '2' | '3' | '4'
number = digit digit*
expr = number (('+' | '-') number)*
;EBNF
Then:
"123+456" expr
Will result in a parse tree left on the stack. The EBNF: name ...
;EBNF expression results in a word with 'name' defined that parses the
given grammar.
You can also do:
<EBNF
digit = '1' | '2' | '3' | '4'
number = digit digit*
expr = number (('+' | '-') number)*
EBNF>
This leaves a parser object on the stack which you can call 'parse' on:
"123" over parse .
Or:
"123" [EBNF
digit = '1' | '2' | '3' | '4'
number = digit digit*
expr = number (('+' | '-') number)*
EBNF] .
The [EBNF ... EBNF] creates an anonymous quotation and calls it. This
is useful for small regexp style grammars:
"123" [EBNF digit=[0-9] => [[ digit> ]] rule=digit+ EBNF] .
>
> Why have you color-coded the "parse" words in the HTML?
The blog was originally hosted on a server that linked to the factor
documentation for some of the words (like 'parse'). The links are dead
now.
Chris.
--
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